Method and apparatus for modulating and demodulating data into a variable length code and a providing medium for implementing the method

ABSTRACT

A SYNC bit inserting section  14  adds a sync signal to a train of codes, after adding a minimum run, said sync signal having a pattern that breaks a maximum run. It is thereby possible to provide a reliable sync signal pattern.

TECHNICAL FIELD

The present invention relates to a modulation a data-modulatingapparatus, a data-modulating method, a data-demodulating apparatus, adata-demodulating method, and a data-providing medium. Particularly, theinvention relates to an apparatus and method for modulating data totransmit the data or record the data on a recording medium, an apparatusand method for demodulating data that has been modulated, and a mediumfor use in transmitting or recording data that has been modulated.

BACKGROUND ART

Data is modulated to be transmitted via a predetermined transmissionpath or recorded on a recording medium such as, for example, a magneticdisk, an optical disk or a magneto-optical disk. Known as one of suchdata-modulating methods is block encoding. In the block encoding, a rowof data is divided into blocks, or units each consisting of m×i bits.(Hereinafter, the units of data will be referred to as “data words.”)The data words are modulated to code words, each consisting of n×i bits,in accordance with an appropriate encoding rule. Each code word has afixed length if i is one (1). It has a variable length if the value ican be selected from a plurality of values. That is, the code word has avariable length when one of values ranging from 1 to imax (the greatestvalue for i) is selected for i. The code generated by the block encodingis a variable-length code (d, k; m, n; r).

It should be noted that the value i is called “constraint length”, andthe value imax is called “maximum” constraint length r. The minimum rund indicates the least number of ones (1s) that may be included in atrain of codes. The maximum run k indicates the greatest number of ones(1s) that may be included in a train of codes.

To record variable-length codes generated as described above, on acompact disk, a mini-disk or the like, NRZI (NonReturn to Zero Inverted)modulation on the variable-length codes. In the NRZI modulation, thevariable-length code is inverted at each one (1) and not inverted ateach zero (0). The variable-length codes subjected to the NRZImodulation (hereinafter referred to as “level codes” are recorded on thedisk.

Inverse NRZI modulation, wherein a level code is changed to when isinverted to “0” or “0” is inverted to “1”, thereby becoming an edge, maybe performed on variable-length codes. In this case, a train of codesidentical to original EFM codes or RLL (1-7) codes can be obtained.These inverse NRZI codes are called “edge codes.”

Let the minimum interval of inverting level codes be Tmin, and let themaximum interval of inverting level codes be Tmax. In order to recorddata at high density in the linear velocity direction, it is desiredthat the minimum code-inverting interval Tmin be long. That is, theminimum run d should be large. In order to reproduce clock signals, itis desired that the maximum code-inverting interval Tmax be short. Inother words, the maximum run k should be small. In view of this, variousdata-modulating methods are proposed.

One example is the data-modulating method known as RLL (1-7) that isused to record data on a magnetic disk, a magneto-optical disk or thelike. The parameter for this data-modulating method is (1,7:2,3; 2). Theminimum code-inverting interval Tmin is 2T, or (1+1)T. This minimumcode-inverting interval Tmin is 1.33Tdata, i.e., (m/n)×Tmin=(⅔)×2. Themaximum code-inverting period Tmax, given as (k+1)T, is 8, or(7+1)T=⅔×8Tdata=5.33Tdata. The width Tw of the detection window, givenas (m/n)T, is 0.67(=⅔) Tdata.

The conversion table for RLL (1-7) codes is, for example, a table shownin the following Table 1: TABLE 1 RLL (1, 7; 2, 3; 2) Data Decode i = 111 00x 10 010 01 10x i = 2 0011 000 00x 0010 000 010 0001 100 00x 0000100 010

Symbol x used in the conversion table is “1” when the next channel bitis “0” and is “0” when the next channel bit is “1”. The maximumconstraint length r is 2.

In the train of channel bits, which has been modulated by the method RLL(1-7), 2T occurs most frequently at interval Tmin, 3T occurs lessfrequently than 2T, and 4T occurs less frequently than 3T. If edge dataitems such as 2T or 3T occurs at high frequency, it helps to reproduceclock signals. If 2T occurs continuously, however, its waveform recordedmay likely to be deformed. (The waveform output of 2T is small and iseasily influenced by either defocusing or tangential tilt.) Further,smallest marks recorded continuously in high linear density may likelybe influenced by external disturbance such as noise, causing errors inthe data that will be reproduced.

The applicant hereof proposed in Japanese Patent Application No.9-133379 that Tmin be prevented from occurring more frequently than aprescribed times. The conversion table for RLL (1-7) codes for use inthis proposed method is, for example, the following Table 2. TABLE 2 RML(1, 7; 2, 3; 3) Data Codes i = 1 11 00x 10 010 01 10x i = 2 0011 000 00x0010 000 010 0001 100 00x 0000 100 010 i = 3 100110 100 000 010

Symbol x used in this conversion table is “1” when the next channel bitis “0” and is “0” when the next channel bit is “1”. The maximumconstraint length r is 2.

In the conversion achieved by using Table 2, the next four data itemsare referred to when the data row becomes “10”, and a code “100 000 010”for preventing the repetition of the minimum run d is given when thedata row of six bits becomes “100110”. The minimum run d may be repeatedsix times at most in the code obtained by this conversion.

To record data on a recording medium or transmit data in a specific way,the data is modulated into codes that can be recorded on the medium ortransmitted in that specific way. The modulated codes may contain adirect-current component. If so, various error signals, such as thetracking error signal for the servo control in a disk drive, are likelyto change or contain jitter. Therefore, the modulated codes should notbetter contain a direct-current component.

The variable-length RLL codes mentioned above, in which the minimum rund is 1 (d=1) and the conversion rates m and n are 2 and 3 (m=2, n=3),are not subjected to DSV (Digital Sum Value) control. In the DSVcontrol, the absolute value of the total sum (DSV) of codes isdecreased, when the train of channel bits is subjected to the NRZImodulation (that is, converted to level codes), and the “1” bits of thetrain (data symbols), i.e., +1 codes, are added, whereas the “0” bits ofthe train, i.e., −1 codes, are added. The DSV can serve to estimate thedirect-current component in the train of codes. To decrease the absolutevalue of the DSV is to reduce the direct-current component in the trainof codes.

In most cases, 2×(d+1) bits are used as DSV control bits. If d=1, fourbits, i.e., 2×(1+1) bits, will be used as DSV bits. In this case, theminimum run and the maximum run can be maintained, and perfect DSVcontrol can be achieved to invert codes and not to invert codes at anygiven intervals.

However, the DSV control bits are basically redundant bits. It is theredesirable that the DSV control bits be reduced in number as much aspossible in view of the efficiency of inverting codes.

Alternatively, 1×(d+1) bits may be used as DSV control bits. If so, twoDSV bits, i.e., 1×(1+1) bits, will be used. In this case, too, perfectDSV control can be accomplished to invert codes and not to invert codesat any given intervals. Nonetheless, the maximum run increases to (k+2),though the minimum run can be maintained. The minimum run must bepreserved by all means as a recorded code, but the maximum run need notbe preserved as such. In some cases, there are formats in which apattern breaking the maximum run is used as a sync signal. (EFM plus ofDVD has a maximum run of 11T, which may increase to 14T to use aspecific format.)

A table of 1,7PP (Parity preserve Prohibit rmtr) codes is available as atable that can achieve DSV control more efficiently, while preservingthe basic function of the RML codes shown in Table 2. The 1,7PP codesare modulated codes, wherein the minimum run is 1(d=1) and the maximumrun is 7(k=7). In each 1,7PP code, the minimum run is prohibited fromrepeating itself and rule is imparted to the elements that correspond todata words and code words.

The conversion table for 1,7PP codes, which the applicant hereofproposes in Japanese Patent Application No. 10-150280, is, for example,the following Table. TABLE 3 1, 7PP (1, 7; 2, 3; 4) Data Code 11 *0* 10001 01 010 0011 010 100 0010 010 000 0001 000 100 000011 000 100 100000010 000 100 000 000001 010 100 100 000000 010 100 000 ″110111 001 000000(next 010) 00001000 000 100 100 100 00000000 010 100 100 100if xx1 then *0* = 000xx0 then *0* = 101″110111 001 000 000(next 010):When next channel bits are ‘010’,convert ‘11 01 11’ to ‘001 000 000’ afterusing main table and termination table.

In Table 3, the minimum run is 1 (d=1) and the maximum run is 7 (k=7).Among the elements sown in this conversion table are uncertain codes. Anuncertain code is either “000” or “101” if two bits of the data row tobe converted are (11), depending upon the code word train thatimmediately precedes the data row. If one channel bit of the immediatelypreceding code word train is “1”, the two bits (11) will be converted to“000” to preserve the minimum run. If one channel bit of the immediatelypreceding code word train is “0”, the two bits will be converted to“101” to preserve the maximum run.

The conversion table of Table 3 is one having a variable-lengthstructure. That is, a code to be converted at the constraint length i=1is composed of three data items, less than the four data items required[2{circumflex over ( )}(m×i)=2{circumflex over ( )}(2×1)=4]. Namely,among the data rows to be converted is a data row that cannot beconverted at the constraint length i. After all, the constraint lengthi=3 must be applied to use Table 3 as a conversion table, or to convertall data rows.

The conversion table of Table 3 contains replacement codes that restrictthe number of times the minimum run is repeated. Data row (110 111), orexample, is replaced by “001 000 000” if the code word train thatfollows it is “010”. If the code word train is other than “010”, thedata row will be converted to “*0*010*0*”. The code word train obtainedafter the data conversion is limited in terms of the number of times theminimum run is repeated. The minimum run can be repeated six times atmost.

The conversion table of Table 3 is based on the conversion rule thatwhen the number of “1s” in the elements of a data row and the number of“1s” in a code word train to be converted are divided by 2, theremainders are the same, either “1” or “0”. For example, the elements(000 001) of a data row corresponds to a code word train “010 100 100”.The data row has one “1”, whereas the code word train has three “1s”.When the number of “1s” in the data row and the number of “1s” in thecode word train are divided by 2, they have the same remainder, i.e.,“1”. Let us consider another example, The elements (000 000) of a datarow corresponds to a code word train “010 100 000”. The data row has no“1”, whereas the code word train has two “1s”. When the number of “1s”in the data row and the number of “1s” in the code word train aredivided by 2, they have the same remainder, i.e., “0”.

In the conversion table of Table 3, the maximum constraint length r is 4(r=4). The conversion code, in which i=4, has a replacement code toachieve the maximum run k of 7 (k=7).

A data row can be modulated in accordance with the conversion table ofTable 3, thereby to perform DSV control on the train of channel bits atprescribed intervals as has been practiced hither to. Nonetheless, therelation between the data row and the train of converted code words maybe utilized to accomplish the DVS control at high efficiency.

As mentioned above, the conversion table may be one based on theconversion rule that when the number of “1s” in the elements of a datarow and the number of s in a code word train to be converted are dividedby 2, the remainders are the same, either “1” or “0”. If so, inserting aDSV control bit “1” indicating “conversion” or a DSV control bit “0”indicating “non-conversion” in the train of channel bits is equivalentto inserting a DVS control bit ”1” in a data bit train to convert thedata bit train or a DVS control bit “0” in the data bit train not toconvert the data bit train.

Assume that three bits “001” need to be converted in Table 3. To inserta DSV control bit at the end of this bit train, the data conversion isrepresented as (001-x), where x is one bit, either 0 or 1. If x is “0”,the conversion table of Table 3 will change to the following: Data Codes0010 010 000

If x is “1”, the conversion table of Table 3 will change to thefollowing: Data Codes 0011 010 100

The code word train may be subjected to NRZI modulation. Then, thefollowing level codes will be obtained: Data Codes Level Codes 0010 010000 011111 0011 010 100 011000

Obviously, the last three bits of each level code are inverse to-thelast three bits of the other level code. This means that DSV control canbe performed on the data row by selecting either “1” or “0” for the DSVcontrol bit x.

In view of the redundancy due to the DSV control, to perform DSV controlon one bit is to perform this control on 1.5 bit. This is because inTable 3, the conversion rates m and n are 2 and 3 (m2, n=3) in the trainof channel bits. To effect DSV control in a RLL (107) table such asTable 1 is to perform the DSV control in the train of channel bits. Inorder to preserve the minimum run, at least two channel bits arerequired as indicated above. The redundancy therefore increases.

In the conversion table of Table 3, DSV control can be carried out in adata row. The DSV control can therefore be effected efficiently.Furthermore, since the repetition of the minimum run is restricted, itis possible to generated codes that can be recorded and reproduced athigh density.

To utilize the conversion table of Table 3 in practice, a sync signalmust be used to identify the start of the data before the train of codesare reproduced. It is desired that the sync signal have a pattern thatdistinguishes the sync signal from any other signal. A plurality of syncsignals must be used in some cases. If so, it is desired that the syncsignals have such patterns that they may be distinguished from oneanother.

As described above, in order to record data on and reproduce data from arecording medium, such as a magnetic disk, a magneto-optical disk or anoptical disk, at high density, it is necessary to select, as a modulatedcode, a code having the minimum run of 1 (d=1), to minimize thedistortion of data at the time of recording and reproducing the data,thereby to inhibit generation of errors, and to use an appropriate syncsignal when 1,7PP codes are selected as one suitable for high-densityrecording and reproduction of data.

DISCLOSURE OF INVENTION

The present invention has been made in view of the foregoing. The objectof the invention is to provide a more reliably pattern for a syncsignal.

The data-modulating apparatus according to the invention comprises syncsignal adding means for adding a sync signal to a train of codes afteradding a minimum run, said sync signal having a pattern that breaks amaximum run.

The data-modulating method according to the invention includes the stepof adding a sync signal to a train of codes after adding a minimum run,said sync signal having a pattern that breaks a maximum run.

The data-providing medium according to the invention provides acomputer-readable program, which causes a data-modulating apparatus toperform a process including the step of adding a sync signal to a trainof codes after adding a minimum run, said sync signal having a patternthat breaks a maximum run.

The data-demodulating apparatus according to the invention comprisessync signal detecting means for detecting, from a train of codes, a syncsignal having a pattern that breaks a maximum run, after detecting aminimum run.

The data-demodulating method according to this invention includes thestep of detecting, from a train of codes, a sync signal having a patternthat breaks a maximum run, after detecting a minimum run.

The data-providing medium according to the invention provides acomputer-readable program, which causes a data-demodulating apparatus toperform a process including the step of detecting, from a train ofcodes, a sync signal having a pattern that breaks a maximum run, afterdetecting a minimum run.

In the data-modulating apparatus, data-modulating method anddata-providing medium according to the present invention, a sync signalhaving a pattern that breaks a maximum run is added to a train of codes,after adding a minimum run.

In the data-demodulating apparatus, data-demodulating method anddata-providing medium according to the present invention, a sync signalhaving a pattern that breaks a maximum run is detected from a train ofcodes, after detecting a minimum run has been detected.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a data-modulating apparatus accordingto one embodiment of the present invention;

FIG. 2 is a block diagram showing another embodiment of the presentinvention; and

FIG. 3 is a block diagram showing a data-demodulating apparatusaccording to an embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of this invention will now be described. In order to clarifywhich means described any claim corresponds to which component used ineach embodiment, the reference numeral designating the means is writtenin parentheses right after the component described. Nonetheless, thereference numeral thus used does not limit the means to that component.

The data-modulating apparatus according to this invention comprises syncsignal adding means (e.g., SYNC bit inserting section 14 shown inFIG. 1) that is designed to add a sync signal to the minimum runcontained in a train of codes. The sync signal has a pattern that breaksthe maximum run.

The data-demodulating apparatus according to the invention comprises async signal detecting means (e.g., SYNC/Sync ID identification section33) that is designed to detect a sync signal from the train of codesafter detecting the minimum run. This sync signal has a pattern thatbreaks the maximum run.

The patterns of the sync signals shown in Table 3 have the followingfeatures, as is shown in Table 4.

(1) (Tmax+1)-(Tmax+1), thus giving 9T-9T. A pattern breaking the maximumrun is continuously generated twice, thereby increasing the detectionability.

(2) Value 2T is applied before giving 9T-9T, thus preventing thegeneration of Tmax, whichever data row has been modulated. In otherwords, a short run is inserted so that no pattern of 8T-9T-9T may appearin the combination of the modulated data row and the data itemimmediately preceding the sync signal to be inserted. Assume thatpattern of 8T-9T-9T appears. In this case, the detection distancebetween the first half of this pattern, i.e., 8T-9T, and the detectedpattern 9T-9T will be 1, increasing the possibility that the detectionability decreases to make detection errors. To prevent this, 2T isinserted. Alternatively, 3T or 4T may be inserted before the 9T-9T forthe same purpose. If 3T or 4T is inserted, however, the redundancy willincrease. Thus, the highest efficiency is achieved when 2T is inserted.

(3) Two bits are arranged before 2T-9T-9T and used as connection bits.This makes it possible to insert a sync signal at any desired positionand to terminate the data at the position where the sync signal isinserted., TABLE 4 Sync & Termination #01 010 000 000 010 000 000 010(23 + 1 channel bits) # = 0 not terminate case # = 1 terminate caseTermination table 00 000 0000 010 100

Assume the conversion table of Table 3 generates a train of code words(i.e., a train of channel bits.) To insert a sync signal at a desiredposition in the train of code words, a termination table may be used, ifnecessary, to terminate, at the desired position, a code that has beengenerated by the conversion table of Table 3 and that is a code having avariable length.

On the case of Table 3, to insert a sync signal at any desired position,a connection pattern is added at the junction of any two adjacent trainsof code words to preserve both the minimum run d and the maximum run d.A sync signal pattern is inserted between the two adjacent trains ofcode words. (The connection pattern may be regarded as a part of thesync signal pattern.) The sync signal pattern thus inserted or givenconsists of 24 bits, which can be divided by the conversion rates, m=2and n=3, leaving no remainders. More precisely, the sync signal patternis: “#01 010 000 000 010 000 000 010”. The first bit # is the connectionbit, which is either “0” or “1” . The second channel bit is “0” topreserve the minimum run. The third and fourth channel bits define 2T.From the fifth channel bit et seq. define two continuous 9Ts, which isused as the sync signal pattern wherein k=8. That is, eight “0s”continuously appear between “1” and “1”. This pattern is repeated twice.The last channel bit of this sync signal pattern, “1”, is determines themaximum run. The last bit of the sync signal pattern is a connection bitof “0”. The last bit serves to preserve the minimum run, d=1, no matterwhichever bit follows this bit.

The termination table and the connection bit # in the sync signalpattern will be described. The termination table is as follows, as shownin Table 4;

-   -   00 000    -   0000 010 100

The termination table must be used when less than four conversion codes,which are not replacement codes for limiting the continuation of theminimum runs define the constraint length. As seen from Table 3, thereare three conversion codes when the constrain length is 1, i=1. Hence,the termination table must be used. If the constraint length is 2, i=2,too, there are three conversion codes and the termination table must beused. If the constraint length is 3, i=3, there are five codes, of whichone is a replacement code and the remaining four are conversion codes.Since there are required number of codes, termination is performed. Ifthe constraint length is 4, i=4, the conversion codes are allreplacement codes and it is unnecessary to taken termination intoconsideration. Hence, (00), i.e., the constraint length i=1 and (0000),i.e., the constrain length i=2, are given to the termination table.

The connection bit “#” of the sync signal is given to distinguish thecase where a termination is used from the case where no terminationtable is used. To be more specific, the first channel bit “#” of thesync signal pattern is “1” when a termination code is used. Otherwise,this bit is “0”. Thus, the connection bit “#” can reliably distinguishthe case where a termination table is used from the case where notermination table is used, at the time of demodulating codes.

The sync signal pattern is defined by (23+1) channel bits and cantherefore be reliably detected. In the case where two or more types ofsync signals are required, (23+1) channel bits are insufficient toprovide these types of sync signals.

Thus, six bits may be added to the above-mentioned 24 channel bits,whereby 30 channel bits are used, generating sync signals of varioustypes. The various types of sync signals will be described below.

The sync signal patterns of two or more types, shown in the conversiontables of Tables 3 and 4, are defined as shown in Table 5. In each syncsignal pattern, the minimum run is preserved and the minimum run cannotbe repeated more than six times as shown in Table 3. Each sync signalpattern is so selected that the maximum run will not be generatedoutside the sync signal detection pattern. These sync signal patternsare connected to a data row in the sane way as is indicated in Table 4.TABLE 5 30 channel - bit Syncs #01 010 000 000 010 000 000 010 000 001#01 010 000 000 010 000 000 010 000 010 #01 010 000 000 010 000 000 010000 100 #01 010 000 000 010 000 000 010 001 000 #01 010 000 000 010 000000 010 001 001 #01 010 000 000 010 000 000 010 001 010 #01 010 000 000010 000 000 010 010 000 #01 010 000 000 010 000 000 010 010 001 #01 010000 000 010 000 000 010 010 010 #01 010 000 000 010 000 000 010 010 100#01 010 000 000 010 000 000 010 100 001 #01 010 000 000 010 000 000 010100 010 #01 010 000 000 010 000 000 010 100 100 #01 010 000 000 010 000000 010 101 000 #01 010 000 000 010 000 000 010 101 001 # = 0 notterminate case # = 1 terminate case Termination table 00 000 0000 010100

As shown in Table 5, if 30 bits are used as sync signal bits, 15 typesof sync signal patterns will be provided in accordance with variousrules. From these sync signal patterns, the following various syncsignal patterns can be determined as will be explained below.

Namely, signal patterns can be selected, any adjacent two of which arespaced apart by a distance of 2 or more. TABLE 6 30 channel - bit Syncs#01 010 000 000 010 000 000 010 000 001 #01 010 000 000 010 000 000 010000 100 #01 010 000 000 010 000 000 010 001 001 #01 010 000 000 010 000000 010 010 000 #01 010 000 000 010 000 000 010 010 010 #01 010 000 000010 000 000 010 100 001 #01 010 000 000 010 000 000 010 101 000 # = 0not terminate case # = 1 treminate case Termination table 00 000 0000010 100

The “distance of 2 or more” means that the two sync signal patternsdiffer from each other at two or more bits when the sync signal patternsare detected (the data reproduced is a level code). The sync signalpatterns shown in Table 6 are those selected to satisfy this conditionat the last six bits. The patterns shown in Table 6 are effective whenmany types of sync signals are required.

The following three sync signal patterns can be selected as DC-free syncsignal patterns. TABLE 7 30 channel - bit Syncs #01 010 000 000 010 000000 010 001 000 #01 010 000 000 010 000 000 010 010 001 #01 010 000 000010 000 000 010 100 010 # = 0 not terminate case # = 1 terminate caseTermination table 00 000 0000 010 100

The word “DC-free” means that 30 channel bits of the sync signal patternhas a DSV value of zero. The sync signal patterns shown in Table 7 areDC-free and each spaced from the adjacent one by a distance of 2 ormore.

The following three sync signal patterns can be selected to form a set,wherein the last bit of each sync signal pattern can be either “0” or“1”. TABLE 8 30 channel - bit Syncs #01 010 000 000 010 000 000 010 00100x #01 010 000 000 010 000 000 010 010 00x #01 010 000 000 010 000 000010 101 00x x: 0 or 1 # = 0 not terminate case # = 1 terminate caseTermination table 00 000 000 010 100

In the set of sync signal patterns, wherein the last bit of each syncsignal pattern can be either “0” or “1”, the last channel bit of eachpattern serves to perform DC control on the next data row converted.Efficient DSV control can be achieved in the sync signal part. Thedata-modulating apparatus effects the DSV control by selecting “1” or“0” for the last bit of each sync signal pattern of Table 8, inaccordance with the DSV value of the following data row. The three typesof sync signal patterns are determined, regardless of the value of thelast bit of the pattern.

An embodiment of the data-modulating apparatus according to the presentinvention will be described with reference to the accompanying drawing.This embodiment is a data-modulating apparatus that converts a data rowto a variable-length code (d,k; m,n; r) (1,7; 2,3; 4).

FIG. 1 is a block diagram showing a data-modulating apparatus accordingto one embodiment of the present invention, which inserts sync signalsat prescribed intervals. The DSV bit determining/inserting section 11performs DSV control on a data row at a given intervals, determines aDSV control bit “1” or “0”, and inserts the DSV control bit at theprescribed intervals. The data row is supplied to a modulation section12 and a SYNC/Sync ID determining section 13. The modulation section 12modulates the data row having the DSV control bits inserted, generatinga train of codes. The train of codes is output to a SYNC bit insertingsection 14. The SYNC/Sync ID determining section 13 determines thepattern of the sync signals inserted into the data row at the prescribedintervals. The data representing the pattern, thus determined, issupplied to SYNC bit inserting section 14.

The SYNC bit inserting section 14 inserts the sync signals determined bythe SYNC/Sync ID determining section 13, into the train of codes inputfrom the modulation section 12. The train of codes, now containing thesync signals, is supplied to an NRZI modulation section 15. The NRZImodulation section 15 performs NRZI modulation on the train of codessupplied from the SYNC bit inserting section 14, converting the same toa train of record waveforms. That is, the NRZI modulation section 15outputs a train of record waveforms. The timing control section 16generates a timing signal. The timing signal is supplied to the DSV bitdetermining/inserting section 11, modulation section 12, SYNC/Sync IDdetermining section 13, SYNC bit inserting section 14 and NRZImodulation section 15, thus controlling the operation timing of thesesections.

The SYNC/Sync ID determining section 13 sets the first 24 codes of the30-code word, i.e., the sync signal pattern of Table 3, to “x 01 010 000000 010 000 000 010.” “x” is determined, depending on the train ofconverted codes that immediately precedes the sync signal inserted. Ifthe immediately preceding data conversion has been effected by the useof a termination table, “x” is set to “1”(x=1). Otherwise, “x” is set to“0”(x=0). That is, “x” is equivalent to a sync signal inserted and hassuch a value as to preserve both the minimum run and the maximum run.

The SYNC bit inserting section 14 inserts the sync signal into the trainof codes, said sync signal being one SYNC/Sync ID determining section 13has determined as mentioned above. After the sync signal has beeninserted into the train of codes, the process starts at the head of theconversion table.

The operation of the present embodiment will be explained.

DSV control is performed on the data row at the prescribed intervals,and sync signals are inserted into the data row at the prescribedintervals. The DSV bit determining/inserting section 11 accumulates theDSV values up to a certain position and calculates a DSV value for thenext interval. Then, the section 11 selects a DSV control bit of “1” or“0” that makes smaller the sum of the accumulated DSV value and the DSVvalue for the next interval. The section 11 inserts the DSV control bit,thus selected, into the data row. The DSV value cannot be determinedfrom the data row only. Thus, the DSV bit determining/inserting section11 uses the conversion table, generating a train of code words from thedata row. The section 11 finds the DSV value on the basis of the trainof code words.

The bit train having the DSV value inserted is modulated (or converted)by the modulation section 12 on the basis of the conversion table. Themodulation section 12 stores data representing the intervals of syncsignals; it modulates the bit train up to a bit close to a sync signal.If the bit train cannot be converted by the use of the ordinaryconversion table, that is, if the termination table of Table 4 must beused, the data showing this fact is output to the SYNC/Sync IDdetermining section 13.

The SYNC/Sync ID determining section 13 stores data representing theintervals of sync signals and determines the value of the first bit ofthe sync signal, i.e., the connection bit, from the condition existingbefore the sync signal was inserted. If the bit train is converted bythe use of the ordinary conversion table, the connection b it is set to“0”. If the bit train cannot be converted by using the ordinaryconversion table and the termination table must therefore be used, theSYNC/Sync ID determining section 13 will refer the termination table,setting the first bit of the sync signal, i.e., the connection bit, to“1”.

Thus, the first 24 bits of the sync signal are determined. The remainingsix bits are set to values and used as Sync ID bits of the sync signal.The Sync ID bits may take one of seven sync signal patterns shown in,for example, Table 6. In each of these sync signal patterns, anyadjacent two bits are spaced apart by a distance of 2.

The sync signals are determined as described above. The SYNC bitinserting section 14 inserts the sync signals into the train of codes.The sync signals may be determined by the use of the termination tablestored in the SYNC/Sync ID determining section 13. In this case, thesync signals, each containing the value obtained from the terminationtable, are inserted into the train of codes by means of the SYNC bitinserting section 14.

Finally, the NRZI modulation section 15 converts the train of channelbits that has been DSV-controlled and that contains sync signals, into arecord code.

FIG. 2 is a block diagram illustrating another embodiment of the presentinvention. As already explained in conjunction with the firstembodiment, modulation and NRZI modulation must be performed in order tocalculate a DSV value. Since each sync signal must be subjected to DSVcontrol and, thus, to NRZI modulation. In view of this, thedata-modulating apparatus may be designed as is shown in FIG. 2.

In the data-modulating apparatus of FIG. 2, the control bit insertingsection 21 inserts a DSV control bit for every prescribed number of bitsin the data row. The data row, now containing the DSV control bits, issupplied to the modulation section 12. The bits of this prescribednumber include sync signals. Hence, the control bit inserting section 21need not insert only one specific number of bits (rather, it may inserttwo or more specific numbers of bits). The modulation section 12converts the data row supplied from the control bit inserting section21, generating a train of channel bits. If the data row cannot beconverted immediately before a sync signal in the modulation section 12,the section 12 will output a signal to a SYNC/Sync ID inserting section22, instructing that the termination table be used.

The SYNC/Sync ID inserting section 22 inserts a sync signal in to themodulated code word at prescribed intervals. The SYNC/Sync ID insertingsection 22 has a termination table. Whenever necessary, the section 22uses the termination table, performing modulation and inserting 30 bitsof the sync signal pattern into the train of channel bits. The train ofcode words, containing the sync signal and the DSV control bit, isconverted to level codes by the NRZI modulation section 15. A DSVbit/SYNC determining section 23 calculates a DSV value from the train oflevel codes supplied to it. At the same time, the section 23 determinesthe pattern of the sync signal. The output of the DSV bit/SYNCdetermining section 23 is a train of record codes and identical to theoutput of the data-modulating apparatus shown in FIG. 1. The timingcontrol section 16 generates a timing signal. The timing signal issupplied to the control bit inserting section 21, modulation section 12,SYNC/Sync ID inserting section 22, NRZI modulation section 15 and DSVbit/SYNC determining section 23. The timing signal controls theoperation timing of these sections.

Next, the operation of the data-modulating apparatus of FIG. 2 will beexplained. The control bit inserting section 21 generates two trains ofbits from the input data row. In the first train of bits, DSV controlbits “1” are inserted at predetermined intervals. In the second train ofbits, DSV control bits are inserted at predetermined intervals. Thesetrain of bits are modulated by the modulation section 12. The modulationsection 12 incorporates a conversion table. The SYNC/Sync ID insertingsection 22 inserts sync signals in the signals modulated by themodulation section 12. The SYNC/Sync ID inserting section 22incorporates a termination table and converts the data row terminated toinsert sync signals, to a train of code words. The train of code wordsis converted to level codes by the NRZI modulation section 15. At thistime, no DSV control bits are determined in the train of channel bits,and two types of level code trains exist. The DSV bit/SYNC determiningsection 23 calculates the DSV value of each train of level codes andselects and determines that train of channel bits which inhibits theaccumulated DSV values. It is at this time that the pattern of syncsignals is determined. The train of code words (a train of channelbits), thus determined, is output as a data row that has beenDSV-controlled.

Then, a data-demodulating apparatus, which is an embodiment of thepresent invention, will be described with reference to the accompanyingdrawing. This embodiment is a data-demodulating apparatus thatdemodulates a data row modulated to a variable-length code(d,k;m,n;r)=(1,7;2,3;4).

FIG. 3 is a block diagram showing a data-demodulating apparatus fordemodulating data reproduced and containing sync signals. Acomparator/inverse NRZI section 31 compare the signals transmitted via atransmission path or the signals reproduced from a recording medium andperforms inverse NRZI modulation on the signals (thereby, convertingthem to edge signals). The edge signals, or digital signals, aresupplied to a demodulation section 32 and a SYNC/Sync ID recognizingsection 33. The section 32 demodulates the digital signals in accordancewith a demodulation table (i.e., inverse conversion table) and outputsthe signals to a SYNC bit extracting section 34. The SYNC/Sync IDrecognizing section 33 detects the sync signals (Sync) inserted atpredetermined intervals. If an inverse conversion termination table,which is one of the termination tables, is used immediately before thesync signals detected, the section 33 supplies the data showing thisfact, to the demodulation section 32. The SYNC/Sync ID recognizingsection 33 recognizes a Sync ID on the basis of the last six bits of thesync signal. The SYNC bit extracting section 34 extracts the syncsignal. A DSV bit extracting section 35 removes DSV control bits fromthe demodulated data row, which have been inserted at given intervalsinto the data row. Thus, the DSV bit extracting section 35 output theinitial data row. A buffer 36 temporarily stores the serial data inputfrom the DSV bit extracting section 35 and output the same at aprescribed transfer rate. A timing control section 37 generates a timingsignal. The timing signal is supplied to the comparator/inverse NRZIsection 31, demodulation section 32, SYNC/Sync ID recognizing section33, SYNC bit extracting section 34, DSV bit extracting section 35 andbuffer 36. The timing signal controls the operation timing of thesecomponents.

The SYNC/Sync ID recognizing section 33 determines the positions of syncsignals from the pattern specific to the sync signals. Since the syncsignals are inserted at prescribed intervals, the section 33 candetermine their positions by counting the intervals. Once the positionsof the sync signals are determined, demodulation is performed on notonly on the data immediately before any sync signal but also on thetermination table. No termination table is required immediately afterany sync signal, and the data can be demodulated by the use of theordinary conversion table of Table 3.

After the data has been demodulated immediately before the sync signalas described above, the SYNC bit extracting section 34 removes the bitsof a prescribed sync signal. Therefore, the SYNC bit extracting section34 is compatible with the demodulation section 32.

The operation of the data-demodulating apparatus will be explained.

The signals transmitted via the transmission path or the signalsreproduced from the recording medium are input to the comparator/inverseNRZI section 31. The signals are compared and converted to inverse NRZIcodes (codes in which indicates an edge). These codes, or digitalsignals, are supplied to the demodulation section 32 and the SYNC/SyncID recognizing section 33.

The demodulation section 32 demodulates the digital signals inaccordance with the inverse conversion table of Table 3. Thedemodulation section 32 has the inverse conversion table of Table 3, butneed not have an inverse conversion table for termination. In thisinstance, the inverse conversion cannot be effected at a partimmediately before any sync signal inserted. The SYNC/Sync IDrecognizing section 33 performs the inverse conversion, nonetheless. TheSYNC/Sync ID recognizing section 33 supplies the sync signals detected,to the demodulation section 32. The demodulation section 32 startsdemodulating in synchronization with the sync signals.

The SYNC/Sync ID recognizing section 33 detects “x 01 010 000 000 010000 000 010” representing 2T-9T-9T, i.e., the sync signal pattern given.This sync signal pattern contains 9T that is a specific to the syncsignal pattern. The sync signal pattern would not be detected from anyother train of data code words. Once the SYNC/Sync ID recognizingsection 33 has detected a sync signal pattern, the sync signals insertedat the prescribed intervals can be detected by means of an internalcounter or the like.

The SYNC/Sync ID recognizing section 33 has an inverse conversiontermination table, which is one of the termination tables. Itdemodulates the code words generated immediately before each syncsignal, in accordance with the termination table. The results of thedemodulation thus effected are supplied to the demodulation section 32.After all, it suffices to set an inverse conversion table in either thedemodulation section 32 or the SYNC/Sync ID recognizing section 33.

The SYNC/Sync ID recognizing section 33 recognizes the two or more syncsignals that follow the 2T-9T-9T, which is a sync signal pattern. Apattern that can be readily detected is selected for each sync signal.

The SYNC bit extracting section 34 removes 30 bits from each syncsignal. Furthermore, the DSV bit extracting section 35 removes DSVcontrol bits inserted at prescribed intervals.

An example of the inverse conversion table is shown in Table 9 presentedbelow. An example of the terminal inverse converse table is shown inTable 10 presented below. TABLE 9 Inverse Conversion Table 1, 7PP-(d, k;m, n; r) = (1, 7; 2, 3; 4) r = 4 Train of Code Words Demodulated DataRow i = 1 101 11 000 11 001 10 010 01 i = 2 010 100 0011 010 000(not100) 0010 000 100 0001 i = 3 000 100 100 000011 000 100 000(not 100)000010 010 100 100 000001 010 100 000(not 100) 000000 i = 3 :ProhibitRepeated Minimum Transition Run length 001 000 000(not 100) 00001000 i =4 :limits k to 7 000 100 100 100 00001000 010 100 100 100 00000000

TABLE 10 Inverse Conversion Table Termination table 000 00 010 100 0000

The minimum run, d=1, can be preserved by determining sync signals andinserted in the way described above. The number of times the minimum runcan be repeated remains limited to six. No run greater than the maximumrun, k=7, would be generated outside the sync signal. If 9T where k=8 isrepeated twice continuously in the sync signal, the sync signal will bemore readily detected. Such a sync signal as shown in Table 6 has seventypes of sync signal IDs, and any adjacent two bits in it are spacedapart by a distance of 2. Thus, the IDs of this sync signal can bereadily detected. Besides these characteristics, DSV control can beeffected on the data bits, making it possible to perform DSV controlwith high efficiency.

The conversion table has variable-length replacement codes, each havingthe minimum run d of 1 (d=1), maximum run k of 7 (k=7), conversion ratem/n of ⅔, and each restricting the number of times the minimum run canbe repeated. The conversion table is based on the rule that when thenumber of “1s” in the elements of the conversion table and the number of“1s” in a code word train to be converted are divided by 2, theremainders are the same, either “1” or “0”. When a sync signal isinserted at a prescribed position in the conversion table, the syncsignal will acquire a unique pattern, without changing the limitednumber of times the minimum run and the maximum ran can be repeated, andwill be readily detected. Hence, the sync signal can be detectedreliably in stability. Further, since the data row terminates, withoutfail, at any position where a sync signal is inserted, the data can bemore easily controlled before and after the sync signal while beingdemodulated. This helps to accomplish stable demodulation of data.

The data-providing medium for providing the computer program for theabove-described process may be a magnetic disk, a CD-ROM, a solid-statememory or the like. Moreover, the computer program may be provided byusing a communication medium such as a network or a communicationssatellite.

INDUSTRIAL APPLICABILITY

In the data-modulating apparatus, data-modulating method anddata-providing medium according to the present invention, a sync signalis added to a train of codes after adding the minimum run. The syncsignal has a pattern that breaks the maximum run. That is, a reliablepattern is imparted to the sync signal.

In the data-demodulating apparatus, data-demodulating method anddata-providing medium according to the present invention, a sync signalis detected from a train of codes after detecting the minimum run. Thesync signal has a pattern that breaks the maximum run. Hence, a syncsignal pattern can be reliably detected.

1-11. (canceled)
 12. A data-demodulating method of demodulating avariable-length code (d, k; m, n: r) having a basic code length of bitsto data having a basic data length of m bits, said method including thesteps of: receiving a train of codes; and detecting from said train ofcodes, a sync signal having a pattern that breaks a maximum run, afterdetecting a minimum run, wherein said pattern is repeated twicecontinuously, wherein said minimum run is repeated no more than sixtimes, and wherein the first bit of the sync signal is “1” when thetrain of modulated codes that immediately proceeds the sync signal isincluded in a termination table used to terminate, at a desiredposition, a code when less than a predetermined number of variablelength codes are available.